The present invention relates to a processing method and apparatus for removing an oxide film formed on a surface of an object and a contaminant to be treated mainly such as a semiconductor wafer, particularly, to a processing method and apparatus for removing a thin oxide film such as a native oxide film formed on a surface of the object such as a semiconductor wafer, and more particularly, to a processing method and apparatus for removing a native oxide film formed in a bottom portion of a fine hole formed on a surface of the object such as a semiconductor wafer.
The present invention is directed mainly to a technique of removing an oxide film formed on a surface of an object such as a semiconductor wafer, particularly, to a technique for removing a native oxide film. Although, the object to be processed-in-the present invention is not limited to a semiconductor wafer, the related art in relation to a technique for removing a native oxide film formed in a bottom portion of a fine hole formed on a surface region of a semiconductor wafer in order to specifically describing the related art is described.
As widely known to the art, processes to form a film on a semiconductor wafer used as a substrate and etching treatments to selectively etch the resultant film in a predetermined pattern are repeatedly carried out in the manufacture of a semiconductor integrated circuit on the semiconductor wafer. During these processes, the substrate is transferred among various processing devices. During the transfer, the substrate is exposed to the air atmosphere, with the result that the oxygen and water within the air atmosphere unavoidably cause a native oxide film to be formed on a surface of the substrate. Formation of the native oxide film causes the properties such as electrical properties of the film on a surface of the substrate to be deteriorated. Where deterioration of the film properties is undesirable in the process for forming a film on the substrate or in the etching process of the film, it is necessary to remove the native oxide film formed on the substrate.
A wet etching is one of the conventional techniques for removing the native oxide film. In the wet etching, the semiconductor substrate (wafer) having a native oxide film formed thereon is immersed in a washing liquid for removing the native oxide film. It should be noted that the line width of a wiring and the diameter of a contact hole formed in the semiconductor wafer are diminished with increase in the scale of integration and miniaturization of the semiconductor integrated circuit. For example, the diameter of the contact hole is 0.2 to 0.3 xcexcm or less (e.g., 0.12 xcexcm). What should be noted is that, since the contact hole has a very small diameter, the washing liquid is unlikely to enter sufficiently the contact hole. Also, the washing liquid once entering the contact hole is not likely to be easily expelled from within the contact hole because of the surface tension of the washing liquid. Under the circumstances, it is difficult for the washing liquid to remove sufficiently a native oxide film formed in a bottom portion of the contact hole.
Where the substrate is subjected to a wet washing, the wall of the contact hole is also etched together with the native oxide film. It should be noted in this connection that the contact hole extends through a plurality of layers formed on the substrate, with the result that the wall of the contact hole consists of a plurality of these layers. What should be noted is that these plural layers differ from each other in the etching rate when subjected to etching with the wet washing liquid. It follows that the surface of the contact hole is rendered irregular after the etching with the wet washing liquid. FIGS. 6A and 6B show in detail the situation. Specifically, FIG. 6A shows that a contact hole 2 for achieving an electrical contact with a drain or source region is formed in a surface region of a silicon substrate W. The contact hole 2, which has a diameter of about 0.2 to 0.3 xcexcm, extends through three layers consisting of a SiO2 xcex1 layer 4 formed by thermal oxidation, a phosphorus-doped glass (SiO2) xcex2 layer 6 formed by a spin-coating method, and a silica glass (SiO2) xcex3 layer 8, as shown in the drawing. A native oxide film 10 is formed at the bottom of the contact hole 2. These SiO2 layers 4, 6 and 8 slightly differ from each other in the etching rate when washed with a washing liquid. It follows that, if the native oxide film 10 is removed by the wet etching, the wall surface of the contact hole 2 is caused to be irregular by the difference in the etching rate noted above, as shown in FIG. 6B. In addition, the washing liquid tends to enter the boundary regions between the adjacent two layers, leading to an over-etching of the boundary regions.
To overcome the above-noted difficulties, it is proposed to employ a so-called dry etching method in place of the wet etching method for removing the native oxide film at the bottom of the contact hole. Japanese Patent Disclosure (Kokai) No. 2-256235 discloses a method of removing a native oxide film by utilizing a NF3 gas (halogen gas) or NH3 gas (basic gas). It is disclosed that the halogen gas or the basic gas noted above is introduced into a process chamber, and the native oxide film is removed by plasma formed within the process chamber. In this technique, however, required is an apparatus for exhausting these two kinds of the special gases (NF3, NH3) leading to a high operating cost. Japanese Patent Disclosure No. 6-338478 discloses another technique. It is disclosed that an H2 gas and an H2O vapor are supplied into a plasma generating section for activation of these gas and vapor. Then, an NF3 gas or a gaseous mixture containing NF3 gas is added to the activated gas and vapor for removing the native oxide film. However, since H2O (steam) is used in this technique, a native oxide film tends to be formed in an amount larger than the amount of the removed native oxide film. As a matter of fact, a native oxide film was not sufficiently removed in the experiment conducted by the present inventor.
In order to resolve the above drawback of the conventional wet cleaning, a method of removing a native oxide film from a subject to be treated using etching gas, i.e., a so-called dry cleaning (etching) method is proposed in, for example, Jpn. Pat. Appln. KOKAI Publication Nos. 5-275392, 6-338478, and 9-106977.
FIG. 14 shows a prior art dry etching apparatus for dry-etching an SiO2 film by the dry cleaning method as disclosed in the above No. 5-275392 Publication. The dry cleaning method for eliminating a native oxide film from a subject to be treated, will now be described with reference to FIG. 14 showing the dry etching apparatus. In the apparatus shown in FIG. 14, an open/close valve 450 is closed to cut off Ar gas from an Ar-gas source 454. Open/close valves 436 and 438 are opened to supply NF3 gas and H2 gas from an NF3-gas source 444 and an H2-gas source 446 to a pipe 432 by controlling their flow rates by means of flow-rate controllers (MFC) 440 and 442. In the pipe 432, both the NF3 gas and H2 gas are mixed at a mixing ratio of 1:2 into a mixed gas having a total pressure of 0.2 Torr. A 2.45-GHz-frequency, 50-w-power microwave is supplied from a magnetron into the pipe 432 via a microwave waveguide 448, and the mixed gas thus becomes plasma therein. A fluorine active species F*, a hydrogen active species H*, and a nitrogen active species N*, which are generated by the plasma, move toward a chamber 410 within the pipe 432 and enter a buffer chamber 430 of the chamber 410. These species are then supplied downstream onto a wafer W placed on a susceptor 412 through a porous plate 428. The wafer W is cooled by a chiller which is supplied from a chiller supply unit 418 and cooled to not higher than room temperature. The active species F*, H* and N* supplied to the cooled wafer W, are adsorbed by the native oxide film on the surface of the wafer W and react to SiO into a product. This product is vaporized and exhausted from an exhaust hole 460 provided at the bottom of the chamber 410 by a vacuum pump 466.
In the foregoing prior art method of removing a native oxide film from the surface of a cooled wafer by fluorine, hydrogen and nitrogen active species F*, H* and N* generated by plasma, which is disclosed in Jpn. Pat. Appln. KOKAI Publication No. 5-275392, NF3 is changed into plasma and thus dissolved into fluorine and nitrogen active species F* and N*, so that no NF3 active gas can be generated efficiently. Since, moreover, H2 gas has difficulties in maintaining the plasma state by itself, it is difficult to secure an etching rate enough to eliminate the native oxide film.
In another method of eliminating a native oxide film by dry cleaning, which is disclosed in Jpn. Pat. Appln. KOKAI Publications Nos. 6-338478 and 9-106977, it is difficult to secure an etching rate enough to remove a native oxide film since H2 gas is used alone.
The present invention aims at resolving the above problems or drawbacks of the prior art method of removing an oxide film such as a native oxide film. According to the present invention, in order to remove an oxide film having a thickness of 10 xc3x85 to 20 xc3x85 from the surface of a subject to be treated, H2 gas and N2 gas are mixed into plasma gas, and NF3 gas (reactive gas) is added to the plasma gas during the flow of active species of the mixed gas. The subject is cooled to not higher than room temperature, and the oxide film on the subject reacts with the reactive gas to form a reactive film. After that, the subject to be treated is heated to a given temperature or higher, and the reactive film is removed from the surface of the subject.
An object of the present invention, which has been achieved in an attempt to solve the above-noted problems, is to provide a method and apparatus for effectively removing an oxide film formed on a surface of an object mainly such as a semiconductor wafer.
Another object is to provide a method and apparatus for effectively removing a native oxide film formed on a surface of an object mainly such as a semiconductor wafer.
Another object is to provide a processing method and apparatus, which do not require a high cost for disposing of an exhaust gas.
Another object is to provide a method and apparatus for effectively removing a native oxide film without newly forming a native oxide film.
Further, still another object of the present invention is to provide a method and apparatus for effectively removing a native oxide film formed at a bottom portion of a fine hole formed in a surface region of an object such as a semiconductor wafer.
Further, still another object of the present invention is to provide a cluster system wherein at least one metal-wiring forming chamber is provided in the above apparatus such that a subject to be treated can be carried in an unreactive atmosphere.
According to a first aspect of the present invention, there is provided a method of removing an oxide film formed on a surface of an object to be processed, comprising the steps of:
forming an activated gas from a N2 gas, H2 gas and NF3 gas;
exposing a surface of the object to the activated gas to bring about a reaction between the activated gas and an oxide film formed on a surface of the object, thereby forming a reaction film; and
heating the object to a predetermined temperature so as to sublimate the reaction film.
Preferably, the oxide film to be removed by the above method is a native oxide film.
Preferably, in the above method, the formation of the activated gas from the N2 gas, H2 gas and NF3 gas comprises the steps of forming a plasma of a mixed gas consisting of the N2 gas and H2 gas and also forming active species, and supplying the NF3 gas into the active species so as to form activated gases of the N2 gas, H2 gas and NF3 gas.
Preferably, in the above method, the formation of a plasma of a mixed gas consisting of the N2 gas and H2 gas is carried out in a quartz-made plasma generating section by introducing a microwave into a mixed gas of the N2 gas and H2 gas supplied to the plasma generating section.
Preferably, in the above method, the predetermined temperature is 100xc2x0 C. or higher.
Preferably, in the above method, the processing using an activated gas is executed in room temperature and, after a supply of the activated gas is stopped, the reaction film is sublimated by heating the object to a predetermined temperature.
According to a second aspect of the present invention, there is provided a processing apparatus for removing an oxide film, comprising:
a susceptor on which an object to be processed is disposed;
a process chamber housing said susceptor; and
a mechanism for removing oxide films formed on a surface of the object;
wherein said mechanism for removing the oxide films include:
an activated gas forming device for forming an activated gas from N2 gas, H2 gas and NF3 gas;
an introducing device for introducing the activated gas formed in said activated gas forming device onto a surface of the object disposed on said susceptor arranged within said process chamber; and
a heating device for heating the object to temperatures at which reaction films resulting from reaction between the oxide films formed on the surface of the object and the activated gas introduced into the process chamber are sublimated.
Preferably, in the above processing apparatus, said activated gas forming device includes:
a plasma generating device for converting the supplied gas into plasma;
a gas supply device for supplying N2 gas and H2 gas into said plasma generating device;
an activated species forming device for converting the plasma generated from the plasma generating device into activated species; and
an activated gas forming device for supplying an NF3 gas into the activated species of N2 gas and H2 gas formed in said activated species forming device so as to form activated gases of N2 gas H2 gas and NF3 gas.
Preferably, in the above processing apparatus, the oxide film formed on the surface of the object is a native oxide film formed by the reaction with the air atmosphere during the predetermined process steps applied to the object.
Preferably, in the above processing apparatus, said activated gas forming device includes:
a plasma generating device for converting the supplied gas into plasma;
a gas supply device for supplying N2 gas and H2 gas into said plasma generating device;
an activated species forming device for converting the plasma generated from the plasma generating device into activated species; and
an activated gas forming device for supplying an NF3 gas into the activated species of N2 gas and H2 gas formed in said activated species forming device so as to form activated gases of N2 gas H2 gas and NF3 gas, and
wherein the heating device for heating the object is for heating the object to temperatures at which the native oxide films formed on the surface of the object react with the activated gas introduced into the process chamber and the resultant reaction films are sublimated.
Preferably, in the above processing apparatus, said plasma generating device is equipped with a mechanism for converting a gas into a plasma by utilizing a microwave.
Preferably, in the above processing apparatus, said activated gas forming device includes:
a pipe made of microwave transmitting material; and
a supply section of a microwave and a supply section of an N2 gas and H2 gas formed at the inlet port of said pipe.
Preferably, in the above processing apparatus, an introducing mechanism for introducing said activated gas onto the surface of the object disposed on the susceptor arranged in the process chamber includes a guide arranged at the outlet port of said activated species forming device for guiding the activated gases of the N2 gas, H2 gas and NF3 gas onto the surface of the object.
Preferably, in the above processing apparatus, those walls of said activated gas forming device, said introducing mechanism and said process chamber which are brought into contact with said activated gas are formed of an electrically insulating material.
Preferably, in the above processing apparatus, said heating device heats said susceptor so as to elevate the temperature of the object disposed on the susceptor to temperatures at which said reaction films are sublimated.
According to a third aspect of the present invention, there is provided a surface treatment method comprising the steps of:
carrying a subject to be treated, which has an oxide on a surface thereof, into a treatment vessel;
evacuating the treatment vessel to produce a vacuum;
introducing gas containing N and H gases into a plasma generation section, generating plasma from the gas, and activating the plasma to form an activated gas species of N and H gases;
causing the activated gas species to flow toward the subject and adding an NF3 gas to the activated gas species to generate an activated gas of NF3 gas;
cooling the subject to not higher than a predetermined temperature; and
reacting the activated gas of NF3 gas with the oxide on the surface of the subject to degenerate the oxide into a reactive film.
Preferably, in the above surface treatment method, the gas containing N and H gases is a mixture gas of N2 and H2 gases, and the method further comprises the steps of:
stopping supply of N2, H2 and NF3 gases into the treatment vessel and heating the subject to a predetermined temperature to sublimate the reactive film, after the step of degenerating the oxide into the reactive film; and
stopping evacuation of the treatment vessel and taking the subject, from which an oxide film is removed, out of the treatment vessel.
According to a fourth aspect of the present invention, there is provided a surface treatment method comprising the steps of:
carrying a subject to be treated, which has an oxide on a surface thereof, into a treatment vessel;
evacuating the treatment vessel to produce a vacuum;
introducing gas containing N and H gases into a plasma generation section, generating plasma from the gas, and activating the plasma to form an activated gas species of N and H gases;
causing the activated gas species to flow toward the subject and adding an NF3 gas to the activated gas species to generate an activated gas of NF3 gas;
cooling the subject to not higher than a predetermined temperature; and
reacting the activated gas of NF3 gas with the oxide on the surface of the subject to degenerate the oxide into a reactive film.
Preferably, in the above surface treatment method, the gas containing N and H gases is a mixture gas of N2 and H2 gases, and the method further comprises the steps of:
stopping supply of N2, H2 and NF3 gases into the treatment vessel and heating the subject to a predetermined temperature to sublimate the reactive film, after the step of degenerating the oxide into the reactive film; and
stopping evacuation of the treatment vessel and taking the subject, from which an oxide film is removed, out of the treatment vessel.
Preferably, in the above surface treatment method, the predetermined temperature at which the subject is cooled, is not higher than room temperature.
Preferably, in the above surface treatment method, the predetermined temperature at which the subject is cooled, ranges from 20xc2x0 C. to xe2x88x9220xc2x0 C.
Preferably, in the above surface treatment method, the predetermined temperature at which the subject is cooled, ranges from 10xc2x0 C. to xe2x88x9220xc2x0 C.
Preferably, in the above surface treatment method, the predetermined temperature at which the reactive film is sublimated, is not lower than 100xc2x0 C.
According to a fifth aspect of the present invention, there is provided a surface treatment apparatus comprising:
a plasma generation section for generating plasma from a plasma generating gas;
a treatment vessel connected to the plasma generation section and including a susceptor on which a subject to be treated is placed;
cooling means for cooling the subject placed on the susceptor to a predetermined temperature;
lifting means for lifting the subject to a heating position in the treatment vessel; and
heating means for heating the subject to a predetermined temperature in the heating position.
Preferably, the above surface treatment apparatus is an apparatus for removing a native oxide film from a surface of the subject to be treated.
Preferably, the above surface treatment apparatus further comprises:
a plasma generating gas introduction section for introducing N2 and H2 gases to the plasma generation section as a plasma generating gas; and
an NF3-gas supply section for adding an NF3 gas to an activated gas species of N2 and H2 gases activated by the plasma generation section and caused to flow toward the subject to be treated, and
an activated gas of NF3 gas is generated by adding the NF3 gas to the activate gas species, and the activated gas is reacted with a surface layer of the subject to degenerate the surface layer.
Preferably, in the above surface treatment apparatus, the predetermined temperature at which the subject placed on the susceptor is cooled, is not higher than room temperature.
Preferably, in the above surface treatment apparatus, the predetermined temperature at which the subject placed on the susceptor is cooled, ranges from 20xc2x0 C. to xe2x88x9220xc2x0 C.
Preferably, in the above surface treatment apparatus, the predetermined temperature at which the subject placed on the susceptor is cooled, ranges from 10xc2x0 C. to xe2x88x9220xc2x0 C.
Preferably, in the above surface treatment apparatus, the predetermined temperature at which the subject is heated at the heating position, is not lower than 100xc2x0 C.
Preferably, in the above surface treatment apparatus, the NF3-gas supply section includes a number of gas exhaust holes formed in an inner wall of the treatment vessel.
Preferably, in the above surface treatment apparatus, the NF3-gas supply section includes a shower head having a number of gas exhaust holes provided in the treatment vessel.
Preferably, in the above surface treatment apparatus, the NF3-gas supply section supplies the NF3 gas to the activate gas species in position at least 20 cm away from an end of the plasma generation section in a direction-of the subject to be treated.
Preferably, in the above surface treatment apparatus, the heating means is heat radiation means provided above the subject to be treated.
Preferably, in the above surface treatment apparatus, the heating means is a heating lamp provided above the subject to be treated.
According to a sixth aspect of the present invention, the above surface treatment apparatus comprises a cluster system including at least one metal-wiring forming chamber, a heating chamber, and a load-lock chamber such that the subject is carried through a carrier chamber in an unreactive atmosphere.
According to a seventh aspect of the present invention, the above surface treatment apparatus comprises a cluster system including at least one metal-wiring forming chamber, a heating chamber, a cooling chamber, and a load-lock chamber such that the subject is carried through a carrier chamber in an unreactive atmosphere.
Preferably, in the above cluster system, the metal-wiring forming chamber is a chamber for forming a film of at least one of Al, Ti, TiN, Si, W, WN, Cu, Ta, TaN and SiN.
Preferably, in the above cluster system, the metal-wiring forming chamber includes means for heating the subject to a temperature of 100xc2x0 C. or higher.